The present disclosure relates to a fixing device configured to fix a toner image on a sheet and an image forming apparatus provided with the fixing device.
As one of techniques to fix a toner on a sheet, a sliding belt type fixing technique is known. A fixing device of this technique includes a rotatable cylindrical fixing belt, a pressing pad facing an inner circumferential face of the fixing belt, a pressing roller putting the fixing belt between the pressing pad and the pressing roller and a heating means to heat the fixing belt. When the pressing roller is driven to be rotated, the fixing belt is driven to be rotated and slid with respect to the pressing pad. The sheet on which the toner is transferred is put between the fixing belt and the pressing roller and conveyed, and the toner is fixed on the sheet. Sometimes, a flat heater having both functions of the pressing pad and the heating means is provided. On the inner circumferential face of the fixing belt, a lubricant is applied in order to reduce friction to the pressing pad.
In the above described configuration, as the pressing pad, the fixing belt and the pressing roller are abraded or deteriorated, a slip between the fixing belt and the pressing roller may occur. When a rotation speed of the fixing belt is decreased owing to the slip, the fixing belt may be abnormally heated locally and may be deformed. In order to prevent the occurrence of such a problem, a measure to detect the rotation of the fixing belt by using a cap attached to an end portion of the fixing belt and to control the heating means depending on the rotation condition is provided.
However, the lubricant applied on the inner circumferential face of the fixing belt may enter between the fixing belt and the cap. Then, a frictional resistance of the fixing belt to the cap is decreased and the cap is not rotated together with the fixing belt. As a result, it becomes impossible to detect the rotation of the fixing belt.
In order to prevent the leakage of the lubricant from the fixing belt, a member made of fluorocarbon rubber is sometimes attached around the entire inner circumferential face of the end portion of the fixing belt.
However, in this case, because the new member is added to the fixing belt, the fixing belt may have a complex structure.